The question "Could Bigfoot have actually existed?" is already answered: yes, they could. Things like them have already been found in the fossil record. Its just a very tall member of the Family Hominidae. (everything from apes to humans)
As for the question of evidence, let's look at fossil and present. Our fossil evidence for Gigantopithecus and Chimpanzees is some teeth and bone fragments. Obviously, that's a slim margin of material that differentiates proven existence, so the lack of evidence here is clearly not the presence of proof of non-existence.
What about present-day evidence? Well, there's a lot of it, actually. Most people have not looked at any of it except for the stuff that was 'debunked' and shown to them as a summary of a digestion of an opinionated account of a story, so we've immediately devalued 'evidence' and this has become an exercise in wold-view affirmation due to the 'backfire effect'. (You will hate and reject any evidence that challenges your categories.) You can't really have a conversation about the quality of the evidence without addressing this.
Let's assume we have addressed this and shown that there's no good forensic evidence for the existence of Sasquatch. You still have to deal with the logical principal of Absence of Evidence. In order to prove that the lack of validated hair, scat, footprints, environmental markers, and bodies demonstrates the absence of these creatures from a given habitat, you would first need to establish a credible base-line for the presence of these data points. Without a verified type-specimen, however, the hair, saliva, scat, and blood samples are categorized as 'contaminated' or 'unknown primate', and the vocalizations and stick structures are credited to people or escaped primate pets.
Finally, eye witnesses. There are so many eye witnesses of these creatures... its just astonishing to read the cross-referenced, curated interviews of these folks. Granted, I'm sure some of them are mis-identification, false recollection, tricks of the light, psychosis, or PTSD, but to say that the Chief of Police or PhD scientist or licenced Therapist who says that he/she watched this thing run across a field in broad daylight for many, many seconds, who then measured the footprints it left behind at 18 inches, was 'hallucinating' the event... I don't get that. Is it responsible to reject all eye-witness accounts because they are 'unreliable'? Personally, I don't think you should pronounce judgement on these accounts until you have at least read a number of them and studied the circumstances of the event and the interview.